Mankind has realized for a very long time that ocean waves contain considerable amounts of energy that could be very useful if a means was available to harness it. In recent times, wave energy measurements have been undertaken by a number of countries. It has been found that a number of sites have an annual average wave energy flux approaching 70 kW per meter of wave crest. This level of energy concentration presents a very exciting opportunity to provide renewable “green” energy in very significant amounts. A mile of shoreline with an annual average energy flux 70 kW per meter of wave crest dissipates almost a billion kW hours of energy every year. If this energy is captured and converted to electrical energy at $0.10 per kW hour it would have a market value of $986 million. It is not reasonable to expect this ideal level of return, but a return in the order of 10% of this amount is still considerable at $98 million per year. The objective of this invention is to provide a means of converting as much as possible of the energy available in waves to electrical energy at a cost competitive with other existing energy sources.
Wave energy conversion systems must successfully operate in a very hostile environment and not succumb to violent storms and the deleterious impact of marine plant and animal life. Further, due to the location of the system offshore, finding a means of delivering the energy output to shore at a reasonable cost is also a demanding technical challenge. Even though the technical challenge is significant, one can be confident a suitable system can be developed if cost is not a constraint. The challenge is to provide an energy recovery system where the life cycle cost of energy delivered is economically viable when all costs and benefits are taken into account including pollution credits. This invention provides solutions that allow delivery of electrical and other forms of energy at economically viable cost levels.
A large number of wave energy recovery systems employing floats have been entertained and many patented in the past. They usually employ floats that are connected to mooring points via two or more mooring lines to ensure the float is not displaced any significant amount horizontally due to wave action. Further, the use of more than one mooring line can constrain a system to unidirectional operation limiting effective response of the system to a small angle of approach of oncoming waves. This disadvantage is overcome if the shape of the float in plan is essentially circular. This circular shape has some disadvantages that become more evident as the size of the float is increased. This invention makes use of a float that is generally cylindrical in shape with a single mooring connection permitting omni-directional operation without loss of performance. Further, the invention provides a means to take advantage of lateral motion of the float that results from the influence of ocean waves that is enhanced if the waves are breaking. This invention could effectively employ circular floats without detracting from system performance in some special circumstances related to site conditions.
Most float systems are targeted for installation well off shore that increases the cost of delivering energy to the shore and increases the cost of mooring because the water depth is greater. This invention recognizes these disadvantages in that it is configured for installation near shore (surf zone) in relatively shallow water. Energy recovery is also increased due to the steeper shape of waves in the surf zone. Shallow water mooring also reduces the risk of damage due to extreme storms in that shallower water tends to dissipate the energy of extremely large waves before they engage the float.
Providing a means to survive the extreme storm conditions at minimum system cost is very challenging. This invention deals with this problem by keeping the float at an elevation approximately level with the wave trough of storm waves allowing the uppermost high-energy portion of the wave to pass over the float. The float is designed to withstand the pressure of submergence created as the wave passes over the float. The storm control system has been given the ability to sense automatically the presence of extreme waves and place the system in a storm standby mode until a storm abates.
Float systems often convert float motion into energy by compressing air and in turn allow the compressed air to flow through an air turbine to convert the energy of compression to mechanical energy. This invention generates pressurized fluid that is directed to drive a variable displacement hydraulic motor (or motors) that in turn delivers mechanical energy to electrical generators or other mechanically driven devices. Heat can be generated directly from the pressurized fluid without the need to convert to mechanical energy by simply allowing the fluid to pass through restrictions. This invention preferably has the fluid energy conversion components located inside the float to minimize the distance hydraulic energy must be transmitted as extended transmission distances incur significant added cost and energy losses. Even though locating energy transformation components within the float is desirable in a number of instances, this invention can be configured to work with a remote and or shore based energy conversion components. One of the primary reasons for keeping the energy conversion components within the float is to facilitate removal of the complete system to a local service dock for maintenance without incurring the need to disconnect fluid conducting lines underwater and run the risk of polluting seawater and incurring the risk of seawater entering the fluid system.
Sea plant and animal life that grows on submerged system components is a serious maintenance issue that all wave energy conversion systems must contend. A successful energy conversion must address the problem by choosing appropriate materials and by providing a means to economically remove build-up of plant and animal life that degrades system performance as time passes.
Several means have been invented for the purpose of converting wave energy into electrical energy, and these seem to fall into the following broad categories;
A. “Rotational” Devices
Devices which directly, or at least early in the process, convert the oscillating motion of the waves into rotational energy, which is then generally used to directly turn a generator. Examples of this category of inventions include: Shoreline installations, such as:                i) Kumbatovic (U.S. Pat. No. 5,789,826, Aug. 4, 1998), which employs a flexible boom system to place a moveable turbine into the most active focal wave zone;        ii) Brown (U.S. Pat. No. 5,808,368, Sep. 15, 1998), which places floats at the end of long shore-based lever arms that pivot in response to the vertical motion of the floats in the waves;        iii) Buonome (U.S. Pat. No. 4,454,429, Jun. 12, 1984), which imposes a series of constrictions upon near-shore waters (which serve to amplify the wave action), and places floats between the constrictions, with lever arms on the shore in a manner reminiscent of Brown;        iv) Hidenori, et. al. (U.S. Pat. No. 5,027,000, Jun. 25, 1991), which uses the, rising and falling of water in open-bottomed cylinders placed near shore to mildly compress large volumes of air and drive an air turbine;        
Near shore installations with foundations on the shore bottom, such as;                i) Eberla (U.S. Pat. No. 5,986,349, May 18, 1998; U.S. Pat. No. 4,206,601, Jun. 10, 1980), which utilizes a vertical pilaster and toroidal float surrounding the pilaster to pressurize air or a fluid as the float moves up and down relative to the pilaster;        ii) Youngblood (U.S. Pat. No. 5,359,229, Oct. 25, 1994), which employs a spherical float telescopically mounted to a secured vertical column, with a chain and counterweight, which turn a drive shaft as the float bobs;        iii) Borgren (U.S. Pat. No. 4,241,579, Dec. 30, 1980), wherein a central support grounded on the ocean floor supports a multiplicity of shafts on which are anchored floats that engage the shaft while bobbing, thereby translating the energy to rotational energy;        iv) Whitticar (U.S. Pat. No. 4,560,884, Dec. 24, 1985), which posits a stationary platform with a float connected to an air compressor, that delivers compressed air while bobbing;        
Open ocean craft, platforms, or largely submerged devices (that also could be located near-shore if desired, or that do not specify a location), such as;                i) Russo (U.S. Pat. No. 4,803,839, Feb. 14, 1989), which mounts a float on a raft and achieves a certain amount of bobbing motion of the float relative to the raft, and mechanically converts this to rotational energy, driving a generator;        ii) Lamberti (U.S. Pat. No. 4,389,843, Jun. 26, 1983), which mounts floats on pivot arms from a boat, and using drive sprockets, gears, and clutches, converts this like-wise to rotational motion in a generator;        iii) Sieber (U.S. Pat. No. 5,394,695, Mar. 17, 1995), which posits an array of floats attached to piston-type pressurization units, connected in series to serially compress a fluid (gas or liquid) to a high pressure to then drive turbines and generators;        iv) Hyun (U.S. Pat. No. 5,854,516, Dec. 29, 1988) which employs a multiplicity of buoys suspended in an array in the ocean, where the bobbing motion of the buoys is converted to rotational energy, driving a liquid compression unit, and using the pressurized liquid to drive a turbine and generator;        v) Gordon (U.S. Pat. No. 4,781,023, Nov. 1, 1988), which employs a floating array of hinged floats whose motion relative to their support arms, or to their multiple segments, can drive a piston-type pressurizing device, producing “mechanical, hydraulic, or electrical power”;        
Most of the purely mechanical transducing devices suffer the limitation of unregulated rotational speed of the generator, rendering the output suitable only for non-critical current applications (usually the charging of batteries). To invert such output to a form suitable for the power grid requires an additional, inefficient step, rendering most of these devices impractical. Those that govern the rotational speed employing some kind of load control simply waste any energy produced in excess of the governed speed, again rendering them somewhat impractical.
The shoreline devices, additionally, are generally massive and ugly, and tend to disrupt the shoreline environment; and the near-shore inventions also pose some such additional visual and environmental problems.
The open ocean inventions that are boat-, raft-, or float-based will tend to dampen the surface waves because of their mass (as will those devices with large storage or generating facilities at or near the surface).
Those inventions that posit floats that are specially-designed or weighted, hinged, or otherwise encumbered are needlessly elaborate and generally more expensive than the within invention. In trying to optimize certain aspects of wave energy collection, their overall practicality is called into question. The floats of the within invention are simple, affordable, and responsive, being somewhat small relative to the wavelength of the average wave, and the overall simplicity of each power-producing module (if assembled into multiple arrays) allows easy maintenance, or module replacement, without taking the entire system down.
B. “Non-Rotational” Devices
These devices variously:    i) Use a pressure transducer on a surface below sea level to directly convert to electrical energy, which again is DC in nature and must be inverted to be applied to the power grid; and pressure transducers have expense considerations inherent within them as well (such as North, U.S. Pat. No. 5,955,790, Mar. 13, 1998);    ii) Collect ocean streaming energy, which is used to drive a turbine; but this suffers from uneven speed of flow (Williams, U.S. Pat. No. 5,592,816. Jan. 14, 1997);    iii) Contain a “slider” or other mass, on floating rails or in a floating cylinder, that moves back and forth when its support tips due to wave motion, and interacts with some means of pressurizing a fluid or driving a mechanism, a device which seems to suffer from frictional and inertial dissipation (such as Rubi, U.S. Pat. No. 4,851,704, Jul. 25, 1989 or Stupakis, U.S. Pat. No. 4,843,250, Jun. 27, 1989);    iv) Utilize wave action to move a permanent magnet past a coil and induce electrical current, which again would be sporadic in nature and suitable only for charging batteries or other electrical storage devices (as in Neuenschwander, U.S. Pat. No. 4,539,485, Sep. 3, 1985);    v) Employ a “liquid flywheel”, or whirling vortex of water yielded from waves passing through a refractive horn and ramp, which drives a turbine; and again may produce energy in a pulsatile fashion (as in Wirt, U.S. Pat. No. 4,152,895, May 8, 1979).